https://www.rmg.co.uk/collections/objects/rmgc-object-632429
Parallel rule | Royal Museums Greenwich
parallel ruleroyalmuseumsgreenwich
https://www.merriam-webster.com/dictionary/parallel%20rule
PARALLEL RULE Definition & Meaning - Merriam-Webster
The meaning of PARALLEL RULE is an instrument for drawing a line parallel to another or a series of parallel lines.
parallel ruledefinitionmeaningmerriamwebster